Process of treating cellulose material



Patented Jan. 26, 1932 UNITED STATES HARRY P. BASSETT, 01 GYNTIHIANA,KENTUCKY PROCESS OF TREATING CELLULOSE MATERIAL No Drawing. Applicationfiled April 18,

This invention relates to a process of treating cellulose material andmore particularly to a process of purifying natural cellulosecontainingfibers, such as cotton linters, wood t; or the like, prior to thepreparation of cellulose products therefrom.

This application is a continuation in part of my application Serial No.269,878, filed April 13th, 1928.

The principal object of this invention is to provide a process ofremoving impurities from and improving cellulose-containing materialwithout substantial injury to the material being treated.

A. further object of this invention is to provide a digestion process ofremoving impurities, such as coloring matter, ligneous material, gums,resins and like impurities from fibrous material, such as wood, cottonlinters or the like, without substantial injury to the cellulose fibersthereof.

Uther objects and advantages of this invention will become apparentduring the course of the following description.

in the preliminary treatment of wood pulp and other cellulose materialfor use in certain branches of the so-called cellulose industry such,for example, as the artificial silk industry, it is common practice totreat raw cellulose-containing material, such as wood, Wood pulp, jute,straw, cotton linters or the like, with a digesting liquor of highconcentration under pressure and at a high temperature, for a relativelyprolonged period and thereafter r removing the digesting liquor from thetreated material, for the purpose of removing impurities present in thecellulose-containing material in order to substantially isolate thecellulose present. Ordinarily, Wood, wood pulp, jute, straw and the likeare treated in a single operation with a relatively strong solution ofan alkali or a hot.sulphite solution. 'lhis treatment is generallydrastic due to the high temperatures, pressures and concentrations ofdigestants employed and it not invariably happens that the celluloseitself is attacked and detrimentally altered in character during thetreatment. Moreover, it frequently is the case that this treatmentcauses coloring matter and other impurities lit) 1929. Serial No.356,308.

to be fixed or set in or on the cellulose fibers so that the removal ofsuch impurities is substantially impossible.

The primary purpose of this invention is p to eliminate thedisadvantages of the digesting processes heretofore employed and toprovide a process of treating cellulosecon taining materials to removeimpurities therefrom in an efficient manner and Without substantialinjury to the cellulose. I have discovered that this purpose can berealized by subjecting the cellulose material to aplurality ofdigestions under controlled conditions of temperature, pressure andconcentration of digestants, as hereinafter specifically described. Bythis process, the impurities present in the cellulose material, such asgums, hulls, resins, low celluloses and the like can be satisfactorilyremoved Without any substantial penetration of the digestant orimpurities into the cellulose fibers, and the cellulose materialsimultaneously whitened to a marked degree.

In its broad aspects, my process comprises subjecting the cellulosematerial to be treated to a plurality of boiling operations or boiloutsthe initial boil-out or boil-outs being conducted at such temperatureand pressure and with such a degree of concentration of the digestingliquor that the impurities present are partially removed without injuryto the cellulose present and the coloring matter or other impurities isnot substantially fixed or set n or on the cellulose fibers. Suchpreliminary treatment is followed by one or more boil-outs preferably atan increased temperature and pressure and with substantially the same ora lower degree of concentration of the digesting liquor. Between theseveral boil-outs; the cellulose material is preferably washed Withoutaccess to air althou h in some instances I have found that satisfactoryresults are obtained by omitting the washing and merely drawing off thedigesting liquor which is replaced with fresh li uor.

n preparing the digesting liquor I may employ numerous compounds ormixtures of compounds. For example, I may employ sodium hydroxide,sodium acid sulfite or the fit) other digestant may be used in thisand/or subsequent boil-outs, as suggested above. If the materialtreat-ed appears to contain an excessive amount of impurities theboil-out may be advantageously carried on under the same temperature andpressure conditions as the first boil-out. However, under ordinaryconditions I have found it advantageus to conduct the second boil-out ata temperature sufficient to create a pressure of from 50 to 125 poundsper square inch. A large portion of the impurities having been removedin the first boil-out, a more complete purification is obtained and thedigesting accelerated by employing a higher pressure in this stage ofthe process. The preferred pressure is approximately 80 or 90 pounds persquare inch. The time of heating the material will vary according to theamount and type thereof, but treatment for from approximately 2 to 4%hours is generally satisfactory.

A certain measure of success is obtained by practicing only twoboil-outs but the preferred practice is to employ another boil-out andin some exceptional cases a fourth boilout. Obviously, the number ofsuch treatments may be further increased but actual practice hasdemonstrated that three, or at most four boil-outs is sufficient forwholly satisfactory results.

After the second boil-out is completed, the cellulose material is eitherwashed with hot water or the digesting liquor removed in the mannersuggested above. Thereafter, if further purification is desired, thematerial is subjected to a further boil-out, the conditions oftemperature, pressure and concentration preferably remaining the same asin the second boil-out except in the case where the second boil-cutconsisted of a second prelimi nary treatment wherein the pressure didnot exceed 50 pounds per square inch. In-other words, the third boil-outshould be conducted at a pressure offrom approximately 50 to 125 poundsper square inch. In this connection, it is to be noted that varioussequences of pressures in the various boil-outs may be employed. Forexample, the boilouts may be conducted at pressures respectively of50,80 and 90 pounds per square inch, or 50, 50 and 80 pounds per squareinch, or 30, 80 and 100 pounds per square inch, the particular sequenceemployed being optional and depending upon the material and condition ofmaterial being treated.

The foregoing illustrative example of the invention will be found togivesatisfactory results under ordinary conditions. However, the processmay be refined in various ways. i For example, the digesting liquorsused in the various boil-outs may be modified in order to particularlyadapt the process to the material being treated. As stated above, whenligneous material such as spruce is used, the first boil-out should beconducted with a digesting liquor which is a particular solvent for theligneous material. the material contains a substantial amount of resins,a digesting liquor which is a solvent for such resins is preferablyused. These modifications will be apparent to one skilled in the art.

As suggested above, the preliminary boilout or boil-outs should beconducted at comparatively low pressures in order to avoid the settingof impurities in or on the cellulose fibers and to prevent substantialdeterioration of the cellulose by the penetration of the fibers thereofby the digestant employed. However, higher pressures may be used in thefinal boil-out or boil-outs since, as I have discovered, the preliminaryboiling treatment described not only removes the major proportion ofimpurities but apparently favorably affects the cellulose fibers so thatthe subsequent higher pressurcs, and attendant higher temperatures, arenot substantially injurious thereto. Such higher pressures areadvantageous not only for the acceleration of the digesting 'actionresulting therefrom but also for the reason that, as I have discovered,the viscosity of the material may be regulated, particularly in theproduction of a product of low viscosity, by the control of thepressures in the final boiling treatment. For example, I have found thatthe degree of viscosity of the product will vary according to thepressure employed in the final boiling treatment, the higher thepressure the lower the viscosity, other factors remaining constant. Thisfeature is of great importance when the process is employed for thetreatment of cellulose material to be used in the manufacture ofartificial silk.

During the final boiling operation or operations at relatively elevatedpressures I have found it highly advantageous to add to the digestingliquor a small amount of a bufier compound in order to preserve a highalpha cellulose content in the final product. Ordinarily 1 or 2 poundsof the buffer compound to approximately 100 pounds of the originalcellulose material to be treated will be found to be satsifactoryalthough a greater or smaller amount may be successfully em ployed. As abuffer compound I prefer to employ a salt of a base-forming metal such.for example, as sodium carbonate, sodium phosphate, potassium carbonate,sodium acetate, or the like. Sulfates should not be employed as bufferssince their use does not produce the desired results.

The following process of treating cotton linters to remove impuritiestherefrom may be taken as illustrative of a specific example of theinvention. While in this process only two boil-outs are described, sincethis number of boil-outs has been found in commercial practice to besufficient for purifying cotton inters, it is obvious that one or moreSimilarly when additional boil-outs may be used, as is advisable whenpurifying certain types of wood pulp. Accordingly, in the preferredpractice of my process in treating cotton linters, bales or bundles ofthis raw material are first broken up by picking them apart in anysuitable manner. A suitable quantity, for example, 100 pounds of thecotton linters are then placed in a digester into which is introduced anaqueous solution of a digestant of the character referred to above,preferably caustic such as caustic soda or caustic potash. The strengthof the caustic solution will vary according to the grade of lintersbeing treated but I have found that from 3 to 10 pounds of caustic,dissolved in water in the proportions of from 10 to 20 pounds of waterto 1 pound of caustic, provides a solution suitable for satisfactorilytreating 100 pounds of linters. In the case of average second cutlinters I prefer to treat 100 pounds of such linters with approximately6 pounds of caustic dis solved in approximately 16 times its weight ofwater.

The thus prepared caustic solution having the linters suspended thereinis then boiled under a pressure ranging from atmospheric pressure toapproximately 50 pounds per square inch for a period of from 1 to 6hours, the actual length of treatment depending upon the pressure andthe grade of stock being treated. I have 'found'that boiling for aperiod of approximately 3 hours under a pressure of preferably from 25to 50 pounds per square inch produces wholly satisfactory results. Inthis preliminary boil-out I find it disadvantageous to employ a pressurematerially in excess of 50 pounds per square inch since such excessivepressure causes the digestant, in this case caustic soda, and impuritiespresent to penetrate the fibers, thereby materially lowering the gradeof the product.

After continuing the boiling for the desired period of time the liquidand the dissolved impurities contained therein are drawn or blown offfrom the digester and the remaining mass of cellulose material is washedseveral times, preferably with water and preferably out of contact withthe air. To the washed material in the digester are then added fromapproximately 5 to 16 pounds, preferably 8 pounds, of caustic dissolvedin from 10 to 20 times its weight in water. The resulting mass is thenboiled under a pressure of from 50 to 125 pounds er square inch for from3 to 10 hours, and preferably 5 hours. As indicated above the actualpressure employed Wlll depend upon the degree of viscosity of the finalproduct desired. During the second boil-out I prefer to dissolve in thedigesting liquor approximately 1 or 2 pounds of a buffer compound,preferably sodium acetate.

After the mass has been treated in the manner described above for adesired period of time the. treating solution is drawn or blown ofi'from the digester and the remaining mass washed several times,preferably with water and preferably out of contact with the air. Thecellulose material is then ready for use in preparing cellulosesolutions or the likeand may be treated according to any of 'the usualmethods for preparing such products.

The foregoing example is typical of the invention when a cellulosematerial having a relatively small content of impurities is to betreated. If, however, a third and/or fourth boil-out is desired it isobvious that such a procedure may be followed. In this event, theconcentrations of the digesting liquors in the first and secondboil-outs are somewhat reduced, the total amount of the digestant beingapportioned according to the number of boil-outs. Moreover, as suggestedabove, should the material to be treated contain a relatively highcontent of impurities, it is often advisable to subject the material totwo preliminary boil-outs insteadof one initial boil-out described inthe specific example of the process set forth above. In this event it ispreferable to conduct the two pre liminary boil-outs under conditions ofrelatively low temperature, pressure and concentration of the digestingliquor. As will be obvious, various other modifications of the processwill be apparent to those skilled in the art.

While I have described in detail the preferred practice of my inventionit is to be understood that various changes in the details of proceduremay be resorted to without departing from the spirit of the invention orthe scope of the subjoined claims.

I claim:

1. The herein described process of treating such material with asolution of caustic at a pressure not in excess of 50 pounds per squareinch, removing the liquid from said material, and thereafter treatingthe material with a solution of caustic and a buffer com pound toregulate the degree of viscosity thereof, said caustic solutions beingof such concentrations as to be capable of dissolving impurities in saidcellulose material but substantially incapable of materiallydeteriorating the cellulose.

2. The herein described process of treat ing cellulose material whichcomprises boiling such material with a solution of caustic at a pressurenot in excess of 50 pounds per mg cellulose material which comprisesboilsquare inch, removing the liquid from said as to be capable ofdissolving impurities in said cellulose material but substantiallyincapable of materially deteriorating the cellulose.

3. The herein described process of treating cellulose material whichcomprises boiling such material with a solution of caustic at a pressurenot in excess of pounds per square inch, treating such material toremove the impurities therefrom, and thereafter treating said materialwith a boiling aqueous solution of caustic and a buffer compound at apressure of from approximately 50 to 120 pounds per square inch for aperiod of approximately from 3 to 10 hours, said caustic solutions beingof such concentrations as to be capable of dissolving impurities in saidcellulose material but substantially incapable of materiallydeteriorating the cellulose.

4. The herein described process which comprises treating cotton linterswith an aqueous solution of caustic at the boiling temperature thereofat a pressure of from approximately atmospheric pressure to 50 poundsper square inch for a period of from 1 to 6 hours, the caustic beingpresent in approximately the proportions of from 3 to 10 pounds ofcaustic to 100 pounds or linters and being dissolved in water in theproportion of one part of caustic to from 10 to 20 parts by weight ofwater, removing the caustic solution from the linters, washing saidlinters, and thereafter treating said linters with a solution of causticat the boiling temperature thereof at a pressure of from 50 to 120pounds per square inch for from 3 to 10 hours, approximately from 6 to15 pounds of caustic being present and dissolved in water inapproximately the proportions of one part of caustic to from 10 to 20parts by weight of water.

5. The herein described process which comprises treating cotton linterswith an aqueous solution of caustic at the boiling temperature thereofat a pressure of from approximately atmospheric pressure to 50 poundsper square inch for a period of from 1 to 6 hours, the caustic beingpresent in approximately the proportions of from-3 to 10 pounds ofcaustic to 100 pounds of linters and being dissolved in water in theproportion of one part of caustic to from 10 to 20 parts by weight ofwater, removing the caustic solution from the linters, washing saidlinters, and thereafter treating said linters with a solution of causticand a buffer compound at the boiling temperature thereof at a pressureof from 50 to 120 pounds per square inch for from 3 to 10 hours,approximately from 6 to 15 pounds of caustic being present and dissolvedin water in approximately the proportions of one part of caustic to from10 to 20 parts by weight of water removing the solution from the treatedlinters, and washing said linters.

6. The herein described process of refining cellulose material to removeimpurities including coloring matter therefrom which comprisessuccessively digesting cellulose material in a closed container underpressure with boiling solvent solutions capable of dissolving impuritiestherein and substantially incapable of materially deteriorating thecellulose material, the initial boiling operation being conducted at atemperature sufficient to cause the solvent solution to boil but notsufficient to create a pressure in said container substantially inexcess of 50 pounds per square inch, and a subsequent boiling operationbeing conducted at a temperature sufficient to create a pressure in saidcontainer in excess of 50 pounds per square inch but not in excess of125 pounds per square inch.

7. The herein described process of refining cellulose material to removeimpurities including coloring matter therefrom which comprisessuccessively digesting cellulose material in a closed container underpressure with boiling solvent solutions capable of dissolving impuritiestherein and substantially incapable of materially deteriorating thecellulose material, the initial boiling opereration being conducted at atemperature sufficient to cause the solvent solution to boil but notsufficient to create a pressure in said container substantially inexcess of 50 pounds per square inch, and the final boiling operationbeing conducted under controlled conditions of temperature and pressureto regulate the degree of viscosity of the cellulose material.

8. The herein described process of refining cellulose material to removeimpurities including coloring matter therefrom which comprises boilingsuch material with a solution of caustic in a closed container at avapor pressure not in excess of 50 pounds per square inch, andthereafter boiling the resulting material with a solution of caustic ina closed container at a vapor pressure. in excess of 50 pounds persquare inch, said caustic solutions being of such concentrations as tobe capable of dissolving impurities in said cellulose material butsubstantially incapable of materially deteriorating the cellulose.

9. The herein described process of refining cellulose material to removeimpurities including coloring matter therefrom which comprises boilingsuch material with a solution of caustic in a closed container at avapor pressure not in excess of 50 pounds per square inch, removing theliquid from said material and thereafter treating the material toregulate the degree of viscosity thereof, said caustic solution being ofsuch concentration as to be capable of dissolving impurities in saidcellulose material but substantially incapable of materiallydeteriorating the cellulose. Y

10. The herein described process of refining cellulose material toremove impurities including coloring matter therefrom which comprisesboiling such material with a solution of caustic in a closed containerat a vapor pressure not in excess of pounds per square inch, removingthe liquid from said material, washing said material, and thereafterheating said material with a solution of caustic in a closed containerto a temperature sufficient to create a pressure in said container inexcess of 50' pounds per square inch to regulate the degree of viscositythereof, .said caustic solutions being of such concentrations as to becapable of dissolving impurities in said cellulose material butsubstantially incapable of materially deteriorating the cellulose.

In testimony whereof I aflix m si HARRY P. B S

ature. TT.

